Ammonium sulphate is a fast acting source of Nitrogen......probably best used sparingly in most cases. It is not touted as a changer of pH, but chemically speaking one could anticipate some little change.

Aluminum sulfate is used to lower pH, but is not a very nice plant additive....it can damage the root systems of many plants.....especially rhododendrons. It would seem to be a "cosmetic" additive to manipulate the colours of some Hydrangeas. "Give the people what they want", being the credo!! The plants seem to be secondary.